1. Field of the Invention
The present invention relates to a heavy oil emulsion fuel of an oil-in-water type. More particularly, the present invention is concerned with an aqueous emulsion composition of a heavy oil having a particular particle size distribution and having a high heavy oil concentration, a low viscosity and an excellent storage stability and an aqueous emulsion composition of a heavy oil comprising a fatty acid distillation bottom or an edible oil, having an excellent storage stability and being nonpollutive.
Furthermore, the present invention relates to a process for producing the heavy oil emulsion fuel described above.
2. Description of the Related Art
In recent years, there has occurred a demand for the development of an alternate energy source as a substitute for petroleum which has been used in the largest quantities as an energy source. This demand is due to the limitation of the oil reserve and an increase in the oil price accompanying the same. Under the above-described circumstances, studies have been made with respect to the conversion of heavy oils, such as oil sand and bitumens, as new fossil fuel resources and distillation residues of petroleum and asphalt, into fuel.
However, these heavy oils are usually an oleaginous material containing about 60 to 70% or, in some cases, 70% or more of a heavy faction having a boiling point of 420.degree. to 450.degree. C. or, in some cases, 450.degree. C. or above, which is usually a vacuum distillation residue. As a result, they do not flow, or have a viscosity as high as tens of thousands of centipoises or more. For this reason, when the use thereof as a fuel is intended without heating them to a temperature as high as 280.degree. to 300.degree. C., not only do problems occur in handling, atomization, etc., but also problems of clogging the piping, etc., of boilers renders them very difficult to use.
These heavy oils have higher residual carbon and nitrogen contents than those of gas oil, kerosine and fuel oil generally used as a fuel and, when used as a fuel, have a serious problem that the contents of the soot and dust and the nitrogen oxides in the exhaust gases are increased.
Under these circumstances, emulsion fuels comprising a heavy oil have been proposed and oil-in-water type emulsions having a high oil concentration have also been studied [see, for example, U.S. Pat. Nos. 4,249,554 (published on Feb. 10, 1981; Assignee: Conoco Inc.), 4,776,977 (published on Oct. 11, 1988; Assignee: The British Petroleum Company p.l.c.), 4,923,483 (published on May 8, 1990; Assignee: Intevep,S.A.), 4,934,398 (published on Jun. 19, 1990; Assignee: The British Petroleum Company p.l.c.), 4,943,390 (published on Jul. 24, 1990; Assignee: Petroleum Fermentations, N.V.) and 5,024,676 (published on Jun. 18, 1991; Assignee: Kao Corporation and Mitsubishi Jukogyo Kabushiki Kaisha), and Japanese Patent Publication-A Nos. 104,434/1978 (published on Sep. 11, 1978) and 97,788/1991 (published on Apr. 23, 1991)].
In these emulsion fuels, however, no study is made on the regulation of the particle diameter of the oil phase comprising the heavy oil. Therefore, it is a matter of course that there is a limitation on the increase in the concentration of the heavy oil component and the storage stability, so that these fuels cannot be said to be satisfactory fuels. In some emulsion fuels, the use of an expensive surfactant in a large amount is essential, which leads to a problem of the cost performance of the fuel, so that such emulsion fuels are unsuitable for practical use. Further, each time the place of origin or composition of the heavy oil varies, the kind or amount of addition of the surfactant must be varied, which renders such emulsion fuels unsuitable for practical use from this viewpoint.
Meanwhile, in view of the problem of environmental pollution, waste oil discharged from fast-food shops and confectioneries, which are waste oils derived from edible oils, and which are believed to be used in an amount of several million tons a year in recent years all over the country, have come to be recovered as a recovered oil. In the future, further improvements in the recovery of the waste oil are expected. However, the development of useful applications of the recovered oil has not been made, so that the development of applications of the recovered oil from the viewpoint of the utilization of resources, has been desired in the art.